The invention relates to a calender arrangement for treating a product web, especially a paper web. The invention relates also to a deflection controlled roll having internal roll sleeve stroke and to a method of fixing an operating position of such a deflection controlled roll when it is being used as an end roll in a stack of rolls of a calender arrangement.
From DE 30 04 913 C2 it is known to use a deflection controlled roll both for the upper and lower end roll of a stack of rolls in a calender, in which deflection controlled roll the roll sleeve is supported by hydrostatic sleeve support elements on a roll axle that is secured against rotation in lateral bearings, and is movable vertically relative to the roll axle, that is to say it is provided with an internal roll sleeve stroke. The intermediate rolls of the stack of rolls are also configured so as to be movable vertically. Since the vertical position of the entire stack of rolls must be preset in some manner during operation, stops are provided for that purpose. The roll axle of each deflection controlled roll accordingly passes through a vertical elongate hole in a bearing side support of the roll sleeve in such a manner that the roll sleeve is movable vertically relative to the roll axle within the range of the elongate hole. Under the influence of the sleeve and loading arrangement, the roll sleeve of one end roll moves in the vertical direction until at both its ends it comes to rest with the stop of the elongate hole against a counterstop associated with the roll axle and thus reaches a defined preset position (operating position) of the roll sleeve and therefore of the entire stack of rolls, and is held in that operating position during operation. A disadvantage therein is that during operation of the calender unavoidable vibrations of the machine parts. intensified by a rigid mechanical stop, are transferred to the roll sleeve and to the entire roll system and may result in an impairment of the product web to be treated. It is a further disadvantage that only one position, namely the outermost eccentric position of the roll sleeve stroke, which is provided by a rigid mechanical stop, serves to preset the operating position. The fact that the roll sleeve is supported in the stop also means that the line load profile has restricted (limited) controllability.
From DE 34 16 210 C2 there is known a roll press having an end roll, in which the roll sleeve is mounted near its end on the associated roll axle. Arranged in the region of the bearings are force sensors, the output signals of which so influence a controller for the supporting forces of the hydrostatic support elements acting upon an internal circumference of the roll sleeve that the detected forces are minimized, that is to say, as small forces as possible are transferred to the roll sleeve by way of the bearings. In the development of that arrangement according to DE 39 09 911 C1, hydraulic force sensors are used. A disadvantage thereof is that such an end roll without internal roll sleeve stroke relative to the roll axle cannot be used as a self-loading deflection controlled roll that enables substantially more precise setting and control of the loading forces, that is to say of the line load profile. A further disadvantage is the complexity of the control system and the limitation to only one vertical operating position of the roll sleeve.
The same disadvantages affect the roll arrangement according to DE 29 43 644 C2 in which the relative heights of the roll axle and roll sleeve of an end roll are so controlled that the roll axle adopts an approximately middle position in the roll sleeve.
From DE 39 18 989 C1 it is known, in a deflection controlled roll, for the vertical extension movement of hydrostatic support elements that bear against the roll axle so as to be vertically displaceable and that act by at least one open hydrostatic bearing pocket against an internal circumference of the roll sleeve to be limited by means of stops. When a stop is reached, the support element is secured mechanically and cannot extend further. This results in a specific positioning of the roll sleeve relative to the roll axle. A disadvantage thereof is that the positioning is effected by the actual transmission of forces for setting the line load and, consequently, alters with the latter, resulting in changes in reference position in dependence upon changes in the transmission of forces.
Finally, from DE 42 03 497 A1 there is known a compensating roll for the pressure treatment of product webs, consisting of a stationary roll core surrounded by a rotating roll sleeve which is supported on the roll axle and is vertically displaceable by means of hydraulic support elements lying next to one another, the support elements being arranged on two diametrical lines of the envelope of the roll axle. As a result of the hydraulic support elements"" being acted upon by pressure medium at specific pressure values, the resulting forces co-operate and enable the longitudinal and sectional deformation of the roll sleeve. A disadvantage thereof is that such a compensating roll is configured without an internal roll sleeve stroke, so that the above-mentioned disadvantages occur in this case also.
The problem underlying the invention is therefore so to configure a calender arrangement so that one and the same device enables positioning of the roll sleeve of a self-loading end roll having an internal sleeve stroke, which carries intermediate rolls, held so as to be displaceable vertically, of a stack of rolls and is thus able to set a desired line load profile in the roll nip precisely, and enables detection and control of the forces acting in the positioning region.
A further problem is to provide a deflection controlled roll which enables positioning of the roll sleeve relative to the roll axle in an operating position without substantial additional expenditure.
A calender arrangement is accordingly provided in which an end roll is configured as a deflection controlled roll having internal stroke and is arranged to be fitted with the device for positioning the roll sleeve relative to the roll axle. In the operating state of the calender, the roll sleeve is held in an operating position by means of the positioning device. The roll sleeve carries displaceable intermediate rolls of a stack of rolls. Mounting the roll sleeve on support elements and on at least one stop element enables extremely precise setting and control of a line load profile in the entire roll nip.
The opposite end roll can also be configured as a deflection controlled roll having internal stroke and which can be equipped in the same manner as the one end roll.
The term xe2x80x9cpseudo-stopxe2x80x9d is intended to show that the position of the roll sleeve relative to the axle is not determined by mechanical components lying next to one another, but that the hydraulic medium film is interposed in the through gap between the stop element and the roll sleeve. The height of the through gap depends upon the pressure of the hydraulic medium that is fed in, which is a measure of the positioning forces.
A deflection controlled roll having internal roll sleeve stroke is provided that enables positioning of the roll sleeve by hydraulic means. The hydraulic stopper operates by virtue of the limited element stroke, which secures it on the roll axle with a selectable stroke, in the manner of an overflow valve, and thus stops and holds the roll sleeve in a selectable operating position. Within the range of the internal stroke, the deflection controlled roll can accordingly be displaced to a predeterminable position and fixed there.
If the hydrostatic bearing pocket of a stopper that has been pushed to the maximum stroke is supplied with a constant oil or pressure medium flow, a pressure can build up in that bearing pocket when the internal circumference of the roll sleeve draws closer to the bearing pocket. The pressure can build up to a predeterminable target value at which the bearing pocket rests against the internal circumference of the roll sleeve with a seal gap of a specific gap height resulting from the flow through the gap corresponding to the target pressure value. If that specific gap height is reduced as a result of external disturbing forces, the pressure in the bearing pocket rises and produces an opposite force. If the specific gap height is increased as a result of external disturbing forces, the pressure in the bearing pocket falls, as a result of which an opposite force is likewise produced.
Such a hydraulically positioned hydrostatic stopper is not involved in the actual transmission of forces. A target oil pressure can thus be so set to obtain a specific rigidity of fixing, that is to say the system is, on the one hand, not too rigid but, on the other hand, is not too yielding. The damping of oscillation can thus be optimized.
The hydraulically positioned hydrostatic stopper in the form of a piston/cylinder unit can also be provided with a piston diameter that is different from that of the actual load transmission elements, that is to say the support elements, in order to be able to influence the supporting forces of those elements further. The same applies also to the sealing edge widths of the hydraulically hydrostatic stoppers.
Rises and falls in pressure in the bearing pocket of a stopper are additionally indicators of undesired radial roll sleeve displacements. The changes in pressure value in the bearing pockets can therefore be measured and used as control signals for regulating the supporting forces of the support elements. If, for example, the pressure in the bearing pocket of a stopper rises above the target pressure value as a result of direct or indirect vertical roll sleeve displacements, that rise in pressure can, when a predeterminable maximum pressure value has been reached, trigger a control signal which can be sent to a controller for the support elements which alters the supporting forces in such a manner that the target pressure value is restored. If the pressure in the bearing pocket falls below the target value, a control signal can likewise be sent to the controller for the support elements when a predeterminable minimum pressure value has been reached, and the controller can alter the supporting forces in such a manner that the target pressure value is restored. The roll sleeve is thus hydraulically clamped at the predetermined operating position and held there.
The effective range of the securing can also be determined by way of a target pressure in a bearing pocket of the stopper. The effective range is firstly the difference between the target pressure and a maximum pressure in the bearing pocket, which can be firmly predetermined by way of a pressure limiting valve in a pressure fluid supply line, and secondly the difference between the target pressure and the minimum pressure in the bearing pocket, which can be determined by means of the selected target pressure. Forces are thus controlled. In that manner, the roll and the roll sleeve can be protected from being destroyed. The target pressure of a stopper can be selected as desired, since it can be taken into account as a value that can be firmly set in the profile calculations, its value not being the result of the oil pressure optimization in the support elements.
It is also advantageous if at least two stoppers are arranged in such a manner that they lie approximately at the quarter points of the roll, because there they produce the smallest profile errors, considering the intermediately supported rolls, when there are departures from a target pressure.
It is also advantageous for the stoppers for positioning the roll sleeve to be incorporated additionally into the roll as independent backward-facing elements having independent pressure fluid supplies.
It is also advantageous to incorporate the deflection controlled roll according to the invention into a calender in such a manner that the stoppers are arranged on the backward-facing side of the roll. In the event of pressure changes, which are admittedly small in troublefree normal operation, local departures from the line loading can thus be minimized.
Further developments and advantages of the invention can be found in the following description and in the dependent claims.
The invention will be explained hereinafter in greater detail with reference to the embodiments shown in the attached drawings.